What is the ruling for a man to wear henna? It is has become a trend nowadays, where a groom wears henna on his hands for his wedding reception.
Alhamdulillah, praise and thanks to Allah for the many countless blessings He has blessed us all with. Blessings and salutations to the Prophet Muhammad PBUH, his wives, his family, companions and all those that follow his teachings to the day of judgement.
Henna is an adornment for women, and not for men. In a hadith from ‘Aisyah R.Anha:
أَوْمَتِ امْرَأَةٌ مِنْ وَرَاءِ سِتْرٍ بِيَدِهَا كِتَابٌ إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم فَقَبَضَ النَّبِيُّ صلى الله عليه وسلم يَدَهُ فَقَالَ: مَا أَدْرِي أَيَدُ رَجُلٍ أَمْ يَدُ امْرَأَةٍ. قَالَتْ بَلِ امْرَأَةٌ . قَالَ: لَوْ كُنْتِ امْرَأَةً لَغَيَّرْتِ أَظْفَارَكِ. يَعْنِي بِالْحِنَّاءِ.
“A woman made a sign from behind a curtain to indicate that she had a letter for the Messenger of Allah (ﷺ). The Prophet (ﷺ) closed his hand, saying: I do not know this is a man's or a woman's hand. She said: No, a woman. He said: If you were a woman, you would make a difference to your nails, meaning with henna.”
Sunan Abu Daud (4166), Sunan al-Nasa’ie in al-Kubra (9311), Ahmad in Musnad (26258)
In ‘Aun al-Ma’bud, it is stated that it is encouraged for women to wear henna.  Al-Sanadi comments on the phrase (لَوْ كُنْتِ امْرَأَةً) in the above hadith, stating its meaning as: “If you celebrate the eminence of being a woman, surely you would wear henna on your hands.”
After establishing the fact that henna is an adornment of women, the next point that we will discuss is the prohibition of a man imitating a woman. From Ibn ‘Abbas R.Anhuma, the Prophet PBUH said:
لَعَنَ رَسُولُ اللَّهِ صلى الله عليه وسلم الْمُتَشَبِّهِينَ مِنَ الرِّجَالِ بِالنِّسَاءِ، وَالْمُتَشَبِّهَاتِ مِنَ النِّسَاءِ بِالرِّجَالِ
Allah's Messenger (ﷺ) cursed those men who are in the similitude (assume the manners) of women and those women who are in the similitude (assume the manners) of men.
Sahih al-Bukhari (5885)
Al-Imam Ibn Battal Rahimahullah said that al-Tabari states that the above hadith contains a fiqh ruling where men are prohibited from imitating women in terms of clothing and adornment which are made especially for women. 
In another hadith, the Prophet Muhammad PBUH banished a mukhannath man for wearing henna on his hands and feet. From Abu Hurairah RA:
أَنَّ النَّبِيَّ صلى الله عليه وسلم أُتِيَ بِمُخَنَّثٍ قَدْ خَضَبَ يَدَيْهِ وَرِجْلَيْهِ بِالْحِنَّاءِ فَقَالَ النَّبِيُّ صلى الله عليه وسلم: مَا بَالُ هَذَا. فَقِيلَ: يَا رَسُولَ اللَّهِ يَتَشَبَّهُ بِالنِّسَاءِ. فَأُمِرَ بِهِ فَنُفِيَ إِلَى النَّقِيعِ فَقَالُوا يَا رَسُولَ اللَّهِ أَلاَ نَقْتُلُهُ فَقَالَ: إِنِّي نُهِيتُ عَنْ قَتْلِ الْمُصَلِّينَ
“An effeminate man (mukhannath) who had dyed his hands and feet with henna was brought to the Prophet (ﷺ). He asked: What is the matter with this man? He was told: "Messenger of Allah! He imitates the look of women." So, he issued an order regarding him and he was banished to an-Naqi'. The people said: Messenger of Allah! Should we not kill him? He said: I have been prohibited from killing people who pray.”
Sunan Abu Daud (4928)
Al-Imam al-Nawawi Rahimahullah states in al-Majmu’:
أَمَّا خِضَابُ الْيَدَيْنِ وَالرِّجْلَيْنِ بِالْحِنَّاءِ فَمُسْتَحَبٌّ لِلْمُتَزَوِّجَةِ مِنْ النِّسَاءِ: لِلْأَحَادِيثِ الْمَشْهُورَةِ فِيهِ وَهُوَ حَرَامٌ عَلَى الرِّجَالِ إلَّا لِحَاجَةِ التَّدَاوِي
“As for colouring both the hands and feet with henna, it is encouraged for those who are getting married for women according to sound hadiths and prohibited for men (to wear henna), except when the henna is used as a medication.” (See al-Majmu’. Dar al-Fikr, 1/294)
The same is stated by al-Imam al-Syarwani Rahimahullah in his Hasyiah of Tuhfah al-Muhtaj written by Ibn Hajar al-Haitami Rahimahullah, it is prohibited for men to wear henna, while it is encouraged for women who are getting married.
According to the above discussion, we are inclined to state that it is prohibited for men to wear henna on his hands or feet and it is encouraged for women to adorn herself with henna. Thus, it is prohibited for men to wear henna, regardless of whether it is because he is getting married or as an adornment. The only exception for this ruling is when he wears henna as medication for certain diseases.
As for wearing henna on one’s hair, there is no issue regarding it for both men and women, for there is a hadith that permits it. Wallahua’lam.